<template>
  <div class="spec-preview">
    <!--空对象.imgUrl不会报错-->
    <img :src="imgObj.imgUrl" />
    <div class="event" @mousemove="handler"></div>
    <div class="big">
      <img :src="imgObj.imgUrl" ref="big" />
    </div>
    <!--遮罩层-->
    <div class="mask" ref="mask"></div>
  </div>
</template>

<script>
  export default {
    name: "Zoom",
    props: ['skuImageList'],
    data () {
        return {
            currentIndex: 0
        }
    },
    computed: {
        imgObj(){
          return this.skuImageList[this.currentIndex]||{}
        }
    },
    mounted () {
        //全局事件总线，获取兄弟组件传递过来的索引值
        this.$bus.$on('getIndex',(index)=>{
          this.currentIndex = index;
        })
    },
    methods: {
        handler(event){         
          let mask = this.$refs.mask;
          let big = this.$refs.big;

          //event.offsetX是 鼠标的left长度
          let left = event.offsetX - mask.offsetWidth/2;
          let top = event.offsetY - mask.offsetHeight/2;

          //约束范围
          if(left < 0) left = 0;
          if(left >= mask.offsetWidth) left = mask.offsetWidth;
          if(top < 0) top = 0;
          if(top >= mask.offsetHeight) top = mask.offsetHeight;

          //修改元素mask的left和top值
          mask.style.left = left + 'px';
          mask.style.top = top + 'px';
          //大图的移动方向与展示图的移动方向相反，是展示图的两倍，所以要两倍移动
          big.style.left = -2 * left + 'px';
          big.style.top = -2 * top + 'px';
        }
    }
  }
</script>

<style lang="less">
  .spec-preview {
    position: relative;
    width: 400px;
    height: 400px;
    border: 1px solid #ccc;

    img {
      width: 100%;
      height: 100%;
    }

    .event {
      width: 100%;
      height: 100%;
      position: absolute;
      top: 0;
      left: 0;
      z-index: 998;
    }

    .mask {
      width: 50%;
      height: 50%;
      background-color: rgba(0, 255, 0, 0.3);
      position: absolute;
      left: 0;
      top: 0;
      display: none;
    }

    .big {
      width: 100%;
      height: 100%;
      position: absolute;
      top: -1px;
      left: 100%;
      border: 1px solid #aaa;
      overflow: hidden;
      z-index: 998;
      display: none;
      background: white;

      img {
        width: 200%;
        max-width: 200%;
        height: 200%;
        position: absolute;
        left: 0;
        top: 0;
      }
    }

    .event:hover~.mask,
    .event:hover~.big {
      display: block;
    }
  }
</style>